Angular and linear position sensors are widely used in automatic control systems as feedback-sensing devices in one or more control loops of the system. In the automotive industry a relatively recent trend is providing control-by-wire in lieu of the more traditional control provided by mechanical linkages, such as cables, rods and the like.
Lower cost, higher performance, and utilization of robust sensing technology are some of the factors that make control-by-wire systems attractive to suppliers of automotive equipment, such as the assignee of the present invention. However, these control-by-wire systems generally require more sensors then were required in traditional systems to provide the appropriate control functionality. Examples of sensors that are needed include sensors for providing linear position measurements. Although there are several technologies available for linear position measurement, these technologies may somewhat fall short in meeting the ever-increasing demands that is necessary to successfully compete in the automotive industry. Examples of such demands include lower costs, lower weight and volume as well as higher reliability and performance.
There are some known sensor design arrangements that use a permanent magnet as the moving part relative to a stationary linear Hall device. Unfortunately, such known arrangements require that at least one of the magnet dimensions (e.g., magnet length) be larger than the measurement range of the sensor. This type of arrangement results in increased sensor cost because of the relatively high cost of the magnet, particularly for applications that require a relatively large measurement range.
Another known sensor design arrangement includes two anti-parallel permanent magnets disposed in a spaced apart relationship with a Hall device positioned there between for linear movement parallel to the line of elongation of the permanent magnets. This type of sensor design tends to be extremely expensive. Furthermore, precise alignment of the permanent magnets is difficult.
One design solution is proposed in U.S. patent application Ser. No. 10/374,133 filed on 25 Feb. 2003, now U.S. Pat. No. 6,998,838 B132, issued 14 Feb. 2006, by Y. Lin and assigned to the assignee of the present application. U.S. Ser. No. 10/374,133 is entitled Single Magnet Linear Position Sensor and describes a linear position sensor assembly which includes a magnetic flux concentrator constructed of ferromagnetic materials configured in a generally rectangular structure including an air gap on one side. A permanent magnet is linearly displaceable along the longitudinal axis of the concentrator. A galvanomagnetic sensing element is disposed in the air gap for sensing magnetic flux passing there through. The sensing element is provided to create an output signal indicative of the measured linear position as the magnet travels along the longitudinal axis of the concentrator.
Although having numerous advantages over known prior art designs, particularly in applications having a relatively short measurement range, the one-piece flux concentrator of the Y. Lin device does not lend itself well to some applications, particularly those having characteristic long and intermediate measurement ranges. For each application dictated variant with differing concentrator size and configuration, new tooling and manufacturing equipment would be required, increasing overall costs. Furthermore, the box-shape configuration can be bulky and difficult to package in some applications. This is due to the necessity of positioning the permanent magnet for linear displacement within the concentrator box.
In view of the forgoing, it would be desirable to provide an improved magnetic circuit that is not subject to dimensional constraints of existing sensor arrangements while providing flexibility in accommodating application specific packaging configurations. It would be further desirable to incrementally reduce sensor costs by providing application specific design flexibility, particularly in the configuration and construction of the flux concentrator.